<?php 
class person{
    public static $type='人类';
    public function show1(){
        // var_dump($this);//object(student)#1 (0){  }
        // echo self::$type,'<br>';
        // echo student::$type,'<br>';   //学生
    }
}
class student extends person{
    public static $type='学生';
    public function show2(){
        // var_dump($this);
        // echo self::$type,'<br>';

        // echo student::$type,'<br>';   //学生
        echo static::$type,'<br>';
    
}

$obj=new person();
$obj=show1();
$obj=show2();
?>